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Choice of retainer

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Choice of retainer

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CHOICE OF RETAINER IN FIXED PARTIAL
DENTURE’S
Introduction
In fixed prosthodontics it is the retainer which provide retention and
resistance against horizontal oblique and vertical dislodging forces.
The selection of retainer plays on important role in success of fix partial
denture and so it becomes very important to select suitable retainer for the
existing situation by keeping physiologic, mechanical hygienic and esthetic
factors in mind.
According to Glossary of prosthodontics (1994) fixed partial denture
retainer is defined as the part of fixed partial denture that units the abutments to
the remainder of the restoration.
Requirements of retainer (Physiologic, mechanical hygienic and esthetics)
1. It should with stand the masticatory forces (Mechanical).
2. It should restore the anatomy of the tooth (Physiologic).
3. It should not be harmful to the pulp (Physiologic).
4. It should improve the aesthetics (aesthetics).
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 Reverse three quarter crowns are indicated on mandibular molars
with severe lingual inclination.
 The seven-eighths partial crown covers seven eighths of gingival
circumference of tooth.
 It is generally indicated for maxillary molars and premolars that
are sound mesially but have extensive carious involvement or a previous
restoration on the distal surfaces.
 The seven eighths crown preparation extends the distal finish line
to the mid facial surface avoiding an unnecessary display of metal on the
mesial surface.
 The mesial half crown is actually a three quarter crown rotated so
degrees preserving the distal surface of the tooth while veneering the
remaining surface.
 It is indicated for distally tilted molar abutment.
Indications:
1. Coronal tooth structure is intact or minimally restored teeth.
2. Sturdy clinical crown of average length or longer.
3. Teeth with normal anatomic crown form i.e. without excessive cervical
constriction.
4. Anterior teeth with adequate labiolingual thickness.
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5. Abutment teeth are in reasonable axial ligament.
6. Short edentulous span.
7. There are average or below average occlusal forces.
Contra indications:
1. High caries index
2. Teeth with extensive core restorations before a partial veneer restoration
can be placed the unveneered tooth surface must be sound.
3. Deep cervical abrasion
If the unveneered surface has deep cervical abrasion it is difficult to
establish a finish line.
4. Short teeth
Teeth with short clinical crowns are not suitable for partial veneer crown.
The difficulty is in establishing adequate retention and resistance form.
5. Bell shape or Bulbous teeth
Teeth severely constricted at the cervical area require more axial reduction
to provide adequate groove length. The additional depth required to place
proximal grooves or boxes can jeopardize pulpal health.
6. Thin teeth
It is difficult to prepare groove of suitable length in teeth with insufficient
buccolingual width without undermining the facial enamel.
7. Poor alignment with path of placement of F.P.D.
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Advantages:
Partial veneer crowns have several advantages over complete crowns.
1. Less tooth reduction – conservation of tooth structure.
2. Having fever margins in the intra cervicular space increases
biocompatibility with supportive tissue – less gingival involvement than
with complete cost crowns.
3. Easy margin accessibility for finishing and cleaning is improved.
4. Complete seating of casting is more easily verified with at least one
margin visible.
5. Complete seating of casting during cementation is enhanced by
diminished hydraulic pressure.
6. Electric pulp testing can be conveniently accomplished on the intact
enamel surface.
Disadvantages:
Partial veneer crowns have the following disadvantages.
1. It is less retentive than complete cast crown.
2. Limited adjustment of path of withdrawal / placement.
3. There is limited display of metal with partial veneer crowns.
4. The partial veneer crown preparation is limited to fairly intact teeth with
normally shaped average length clinical crown.
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Full veneer crowns
They are of three types
1. Complete metal veneer crowns
2. Metal ceramic crowns
3. All ceramic crowns
General indications:
1. It should be used on teeth which demands maximum retention.
2. It should be used when abutment tooth is small or when the edentulous
span is long.
3. Porclian Jacket crown or porcelain fused to metal crowns are used
where high esthetics is required.
4. When all axial surfaces of the teeth have been affected by
decalcification or caries and are restored, a full veneer crown should be
used.
Contra indication:
 Poor oral hygiene
Complete metal veneer crown
Indications:
1. Any posterior tooth in nonesthetic zone with existing restoration unable
to withstand normal occlusal forces.
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3. Combination of metal and porcelain
A cast core for a jacket.
e.g. Richmond crown
4. All plastic – dowel processed in acrylic material.
5. Combination of metal and plastic core replacement
Detached dowel crown (Davis)
All porcelain crown with a post that is detached and can be placed on a
prepared root end by cementation of both the post in the root and the
cementation of crown on the post.
Indications:
1. When impossible to restore crown by other means so that vitality can be
maintained.
2. Mostly on anterior teeth, occasionally on posterior teet.
3. When there is normal occlusal relationship.
4. Sufficiently long and thick root structure.
5. Only when periapical and periodontal conditions are favourable.
Contraindications:
1. Heavy and close bite cases.
2. Poor oral hygiene.
3. Patients with parafunctional habbits.
4. Thin narrow roots.
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Advantages:
1. Esthetics.
2. Adequetely strong.
3. Permits alignment with other teeth.
4. Good tissue adaptability.
5. Easily removed for treatment of required.
Disadvantages:
1. Tooth must be non vital.
2. Weakening of root face and canal by enlarging.
Detached post crown with a cast base
 When the coronal portion of the remaining tooth is missing to a
point below gingiva and it is impossible to adapt the crown and root face, a
cast metal base is interposed between the base of the crown and root face.
 This cast base is rigidly attached to the dowel.
Indications:
1. Tooth broken or destroyed by caries to a point subgingivally.
2. Mostly anterior teeth, occasionally bicuspids.
3. In cases with heavy bite.
4. Sufficiently long or thick roots.
5. All periodontal factors favourable.
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 The restoration consists of one or more pontics supported by thin metal
retainer placed lingually and proximally on the abutment teeth.
 These prosthesis rely in part on adhesive bonding between etched
enamel and the metal casting.
 They are held in place by resin which locks mechanically into
chemically etched enamel and into microscopic undercuts in castings.
1. The Rochette type – Uses small perforation in the retainer sections for
restoration and is best suited for anterior bridges.
2. Maryland bridge, reported to have improved bonding strength. Instead
of perforations, the tooth side of framework is electrolytically etched
which produces microscopic undercuts. It can be used for both anterior
and posterior bridges.
3. The Sockwell type suggested design incorporating both perforations and
etching of metal.
This perforated type (Rochette) can be etched on the tooth side of metal
retainer to provide microscopic undercuts for added retention. This is
especially important in areas where perforations cannot be placed such
as proximal surface. The etched metal type (Maryland) can be improved
by adding perforations to provide both types of retention.
Indications:
1. Retainer of fixed partial denture for abutments with sufficient enamel to
etch for retention.
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Disadvantages:
1. Longevity of prosthesis is questionable – Debonding rate increases with
time.
2. Higher dislodgement rate with posterior resin retained fixed partial
dentures.
Indications for multiple retainers
1. Abutment teeth with short roots.
2. Lack of sufficient bone support.
3. Density of alveolar bone.
4. Excessive length span.
5. Excessive lever arm action because of shape of anterior arch.
6. Distal extension of pontic for increased function.
7. Replacement of a missing cuspid.
Summary and Conclusion
The objective in selection of retainer whether it involves a single tooth,
several teeth or complete restoration of masticatory mechanism, it should
restore and maintain function of dental arch. It should be therefore both
restorative and preventive.
To accomplish this objective preventive as well as theraputic measures
should be utilized. The efficiency in selecting the retainer depends on the
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